The city of Calgary, Alberta has recently installed a $400,000 traffic monitoring system on a stretch of highway known as the Deerfoot Trail. And to track the movement and progress of vehicles it monitors the Bluetooth signals coming from mobile phones, headsets, or built-in entertainment systems.

Fifteen sensors in total, spaced out along the route, keep track of various Bluetooth device's MAC addresses so they know how long it takes vehicles to travel certain distances. And using special algorithms Bluetooth signals from pedestrians or other stray sources are ignored, allowing the system to calculate a fairly accurate real-time estimate of drive times which are displayed to drivers via signage.

But the paranoid needn't worry. The system has no access to the actual messages or data in the encrypted Bluetooth signals, and doesn't need to relate them to a specific vehicle to work. So there's no tracking going on at all. Although, there's no reason such a technology couldn't be used to keep an eye out for drivers with a lead foot. [CTV News Calgary via SlashGear]